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NC-2009 EAp2:Minimum Energy Performance

Baseline Fan Power Heat Recovery

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Matt Scott
Engineer
N.E. Fisher & Associates, Inc.
LEEDuser Basic Member
12 thumbs up

I have a few questions on baseline fan power taking credit for heat recovery in the proposed building. 1. Say I have heat recovery in my proposed system, but it is not required in my baseline system. Do I or don't I get to take credit for the added proposed fan power by adding the heat recovery device pressure drop to the baseline fan power calc? Table 1.4 Air-Side HVAC says: •only if modeled in Baseline per G3.1.2.10 2. Say I have an energy recovery unit exhausting 1000 CFM at 0.5" external static and supplying 1200 cfm at 0.3" external static. How do I properly account for the different CFMs and static pressures? Should I just sum the static pressures and only input 1000 CFM at 0.8"?

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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 08/28/2014 - 15:31

1. You can only take the heat recovery adjustment if there is heat recovery required in the Baseline. If heat recovery is not required then you do pay a penalty for the added fan power. This makes sense as the extra fan power is a reality of choosing to add heat recovery to the Proposed system. 2. It should be modeled as designed. Have you entered it in the software as designed? Not sure what software you are using and this could be a specific modeling question that may be better to address to a different discussion forum. You should not sum the static pressures.
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Matt Scott
Engineer
N.E. Fisher & Associates, Inc.
LEEDuser Basic Member
12 thumbs up

Thu, 08/28/2014 - 15:47

1. Understood. I see your point and agree. 2. I'm using HAP. For Heat Recovery it only allows you to input a KW to turn the wheel and its thermal efficiency. One of the ERUs on the job is scheduled as follows: Supply Fan= 4700 CFM at 0.35" external static pressure, 2.05 BHP Exhaust Fan= 4000 CFM at 0.6" external static pressure, 1.59 BHP If I was required by Appendix G to model this heat recovery for a baseline system, how would I determine the allowed baseline fan power in this case?
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Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 08/28/2014 - 16:11

Do not know HAP real well beyond evaluating the input and output reports we see when doing LEED reviews. A specific "how to model something question" should be directed to HAP support since you pay for it anyway. This system would not be required to have heat recovery since the cfm is below 5,000. The baseline fan power is based on the supply air cfm and the result includes the all fans including the exhaust. If required to have heat recovery you also include the heat recovery pressure drop adjustment.
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Matt Scott
Engineer
N.E. Fisher & Associates, Inc.
LEEDuser Basic Member
12 thumbs up

Thu, 08/28/2014 - 17:31

But in this case what would be the heat recovery pressure drop adjustment? Just the outdoor air component? 4700 CFM at 0.35" static? Is baseline heat recovery assumed to be "ideal" with no additional fan energy and only pressure drop across a wheel?
Profile picture for user sheffer
Marcus Sheffer
LEED Fellow
7group / Energy Opportunities
LEEDuser Expert
4454 thumbs up

Thu, 08/28/2014 - 18:05

The pressure drop adjustment is based on the pressure drop across the heat recovery wheel which comes from the manufacturer.

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